Esters of paraffin phosphonic acids



Patented Mar. 26, 1946 UNITED STATES PATENT OFFICE asrsas OF man-rm rnosrnomc ACIDS Gennady M. Kosolapoif, Dayton, Ohio, assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawingr Application March 24, 1945, Serial No. 584,727

13 Claims.

the lower alcohols and more easily hydrolyzedv than esters of the phosphonic acids with the higher alcohols. Since higher alkane phosphonic acids or their ammonium or alkali metal salts possess very good surface active properties, the dibutyl esters of phosphonic acids of from, say, 8 to 18 carbon atoms, are particularly useful as intermediates in the production of wetting-out agents, detergents, etc. Dibutyl esters of such higher alkane phosphonic acids are also advantageously employed as additives to lubricants for the purpose of modifying viscosity and at the same time imparting extreme pressure resistance to the same. The higher alkane esters, i. e., the dibutyl esters of paraflin phosphonic acids having at least 8 carbon atoms, but less than 19 carbon atoms in the acid portion of the molecule, are particularly valuable as plasticizers for resinous materials. Certain of the esters have the property of imparting a substantially permanent softening effect to fibrous materials.

As far as I have been able to ascertain, the only method which has been heretofore employed for the preparation of the dibutyl esters is that disclosed by Arbuzov and Arbuzova (J. Russ.

Phys-Chem. Soc. 62, 1933 (1930)), wherein there is reported the preparation of dibutyl n-butanephosphonate by reaction of trlbutyl phosphite with n-butyl iodide. The reaction was conducted in a sealed tube at a temperature of about 150 C. and the phosphonate was obtained in a yield of about 58%. When attempting to prepare the higher alkane phosphonates employing alkyl halides of 6 or more carbon atoms by the method disclosed by Arbuzov et al., the reaction was found to be so sluggish as to make this process of no economic value. The production of the higher dibutyl paramn phosphonates is further complicated by the fact that all of the intermediate addition product does not decompose during the reaction:

a r wocmmi also:

In the above reaction x is a halogen. The did!- culty with which the intermediate phosphonium compound is formed and decomposed appears to be directly responsible for the low yields. The presence of the phosphonium compound in the reaction mixture has also a further disadvantage. During fractionation, for isolation of the dibutyl 'paraflln phosphonate, the presence of the intermediate phosphonium compound appears to lead to troublesome decomposition of the desired product, even at oil-pump vacua (2 or 3 mm. Hg).

Accordingly; the Arbuzov et al, method, referred to above, could not be used for the commercial preparation of higher paraiiin phosphonates, i. e., for the dibutyl esters of paraflin phosphonic acids in which hydrocarbon radical contains at least six carbon atoms.

Another known method for the preparation of esters of certain paraflin phosphonic acids involves the reaction of sodium diethyl phosphite 20 and an alkyl halide. The diethyl esters of methorganic liquids, except ether, this method presents difliculties in that it is almost imperative to use hot anhydrous ether as solvent, which material also colloidally disperses some of the sodium halide generated by the reaction. The commercial use of ether as a solvent is also undesirable because'of the fire hazard and because of the dimculty encountered in maintaining anhydrous con,- ditions when operating on a commercial scale. The use of sodium diethyl phosphite is additionally complicated by the fact that the hygroscopicity of this ester prohibits its ready handling except in specially designed equipment. Also, the diethyl phosphonates were found to be separable from the reaction products only with dimculty because their susceptibility to hydrolysis prevents washing out the sodium halide with water; hence, separation of the diethyl phosphonates necessitates centrifuging for the removal of the colloidally dispersed sodium halide. In many instances even prolonged centrifuging was found to be ineffective for complete removal of the inorganic salt. These older methods were, therefore, sultable for laboratory preparations only.

New I have found that when sodium dibutyl phosphite, instead of sodium diethyl phosphite, is employed for the preparation of esters of paraflin phosphonic acids, the above disadvantages are obviated. Reaction may conveniently be effected in such relatively high boiling solvents such as hexane, xylene, toluene, petroleum ether or benzene. Sodium dibutyl phosphite is substantially non-hygroscopic; hence, no special precautions need be observed in its preparation, handling and storage. The resulting dibuty paraflin phosphonates are not hydrolyzed by washing with water; consequently, the by-product, sodium halide, can readily be removed therefrom simply by washing the reaction product with water. The present method, involving the reaction of sodium dibutyl phosphite and any alkyl halide for the preparation of dibutyl paraffln phosphonates, enables the production of the dibutyl phosphonates in yields varying from, say, 75% to 95% over a period a few hours at temperatures 01' from.

room temperature to 150 0. without the necessity of employing pressure vessels. These results, as has been stated above, are not obtainable when working with tributyl phosphite.

i In preparing the dibutyl parafiin phosphonates according to the present invention, I prefer to operate substantially as follows: Approximately molecular equivalents of sodium dibutyl phosphite and an allcyl halide, i. e., an alkyl bromide, iodide or chloride, are mixedtogether in an inert solvent at temperatures between room temperature to 150 (3., until separation of sodium halide is substantially complete. The initially separated sodium halide appears in colloidal form; however, due to the conditions of reaction employed, the

' colloidal sodium halide rapidly coalesces tothe crystalline form which readily separates from the reaction mixture. Accordingly, the endpoint can readily be observed by momentarily discontinuing the agitation, and noting the clarity of the reaction mixture. Cloudiness of the reaction mixture, due to the presence of colloidal particles oi sodium halide, therefore, shows that the reaction is incomplete. At the end of the condensation there is evidenced a clear separation of the crystalline sodium halide from the other reaction constituents, the sodium halide settling to the bottom of the reaction mixture and the supernatant liquid being essentially unclouded, Substantially complete separation of the sodium halide usually takes place within a period of from 2 to 3 hours, although for the preparation of the higher paraffln phosphonates a somewhat longer reaction time isdesirable. When employing refluxing temperatures, even with the C16 and C18 halides, a period 01' from 5 to 6 hours generally is suflicient for complete reaction. The temperature employed for the reaction varies with the nature of the alkyl halide employed as well as with the reaction time. With the lower alkyl halides lower temperatures are advantageously employed; 101' example, for the preparation of dibutyl methanephosphonate, reaction is eilected simply by stirring together at room temperature in an inert sol've nt substantially equimolar quantities of sodium dibutyl phosphite and a methyl halide. With the higher alkyl halides, refluxing temperatures at atmospheric pressure are advantageously employed.

Upon complete separation of sodium halide from the reaction mixture, i. e., at the end of the reaction, the mixture is allowed to attain room temperature it heating has been employed. and is then washed thoroughly with water in order to remove the sodium halide. The organic layer is then separated, the solvent is removed from the organic layer by distillation under reduced pressure, and the residue then distilled in vacuo in a fractionating apparatus. One fractionation generally yields the dibutyl paramn phosphonate in substantially pure form. The

solvent employed may be hexane, heptane, petroleum ether, xylene, benzene, toluene or any other liquid which is a solvent for both the sodium dibutyl phosphite and the alkyl halide and is inert under the reaction conditions. When working with those alkyl halides which are liquids, there may be employed an excess of the alkyl halide instead of the inert solvent or diluent, the alkyl halide itself serving as the solvent. In this case reaction may also be carried out in the absence of either an excess of alkyl halide or an inert solvent, equimolar quantities merely being stirred together at ordinary or increased temperatures, i. e., at temperatures of up to 150 C.

The present invention thus provides a highly emcient method for the production of dibutyl esters of paraifin phosphonic acids having from 1 to 18 carbon atoms. The present invention also provide for industry a series of highly valuable, stable, phosphorus-containing organic compounds, i. e., the dibutyl esters of paraflin phosphonic acids of from 8 to 18 carbon atoms. These esters differ from the known dibutyl butanephosphonic acid in that they are readily converted to free, higher paraflln phosphonic acids or their salts, which materials are highly useful in surface-active compositions. The present dibutyl higher paraflin phosphonic esters are advantageously employed as plasticizers, lubricant addi-.

Preparation of sodium dibutyl phosphite.-

Metallic sodium (4.6 g.; 0.2 atom) was placed into a three-necked round bottom flask, provided with a dropping funnel, a sealed stirrer and a reflux condenser closed with a calcium chloride tube; 300 cc. of dry hexane was placed into the flask and, while the liquid-was being gently refluxed with agitation, dibutyl phosphite (39.0 g.; 0.2 mol) was added dropwise during a period of from 20 to 30 minutes, after which the refluxing and stirring were continued until the sodium was completely dissolved.

Preparation of dibutyl n-heranephosphonate.-- To the sodium dibutyl phosphite. prepared as described above, there was added 33 g. (0.2 mol) of n-hexyl bromide during a period of from 30*to 45 minutes and the mixture was stirred with gentle reflux for 5 to 6 hours. Separation of sodium bromide generally began after 15 to 20 minutes and was completed in about six hours. The reaction mixture was then allowed to stand overnight and washed thoroughly with water. The organic layer was then subjected to distillation under reduced pressure for removal of the solvent and any unreacted materials. Fractionation gave 52 g. (93% yield) of substantially pure dibutyl -n-hexanephosphonate, B. P. 182-184 C./20 mm., 11,, 1.4332, d4 0.9366.

Hydrolysis of dibutyl n-hexanephosphonate by refluxing 50 g. of the same with cc. of concentrated hydrochloric acid for a time of approximately 15 hours gave substantially a 100% theoretical yield of crude n-hexanephosphonic acid; the pure compound, M. P. 104.5" C. to 106 C. was obtained by recrystallization of the crude product.

Following the procedure described above for the preparation of dibutyl n-hexanephosphonate, but using other n-alkyl bromides instead of nhexyl bromide, there was obtained the series of dibutyl parailin phosphonates shown in the table Emma 2 which follows: This example shows the employment of dibutyl MR mgutyllalkgne Boiling p int "D" d" Ylicg't p m e Obs. Colo m 131-0 11 1. 4238 0. 9023 09.00 59.13 18 100-2 20 1.4302 0.9402 one 00.4 I so 101-9 11 1.4313 0. 0428 12.00 1200 88 182-4 20 1.4332 0.9300 11.11 11.00 93 188-90 11 1.4355 0. 9313 8220 82.22 13 147-8 2 1.4310 0. 9202 sass scan 70 150-01 2 1.4391 0.9250 90.98 91.45 09 1 S'Siii as 12 3383231 323112.1311: iii-*3 3 1 3; 1 g 52 3133315 22311: 24% 5 114499 019031 132.0 133.02 15 The dibutyl parafiln phosphonates shown in -tetradecanephosph'onate as a plasticizer for varithe above table were obtained according to the ous synthetic resinous materials. The following reaction; solutions of the resins were prepared: i ht r 1. A solution consisting of 10 parts by we g R I l MB of a polyvinyl butyral resin known as "Butvar Na 0 and 90 parts by weight of ethyl alcohol. I have found that R may be any lky radical 2. A solution consisting of 10 parts by weight of from 1 t0 8 ca atoms, branched of ethyl cellulose and 90 parts by weight of xylene. branched, i.. a. met yl. y pr pyl, isomopy 3. A solution consisting of 20 parts by weight y isobutyl nmy i oamyl n-h Y of nitrocellulose and 80 parts by weight of a mixhyl uty nptyl, nc y i -octyl, z-ethylture consisting of 40% of butyi acetate, 20% of heXyL n-n ny iso-nonyl, n-d yl. n L m ethyl acetate, 10% of ethyl alcohol and 30% of n-dodecyl, etc. I have also found that primary t L alkyl halides are more reactive in the condensa- 4 A solution consisting of 50 parts by weight tion than are th Secondary alkyl helidesof pentaerythritol-phthallc anhydride alkyd resin cordingly. the pr ry alkyl halides are pref d which had been modified with 80% linseed oil in the pres n reaetioh- Instead employing a and 50 parts by weight of mineral spirits. alkyl bromides. I may use t e or espo d n To each of the above solutions there was added alk i i e r the corresponding lkyl ehlO- an amount of dibutyl tetradecanephosphonate rides. Howev r, h alkyl chlorides do n P which was equivalent to 20% by weight of the ticipate in the rea ti n as adi as do the weight of the solid resin. The ester dissolved iodides and the bromides, and accordingly, w n 0 readily without residue into each of the solutions. sing he yl chl id s m wha lon r Films cast from each of the ester-containing solueetion Periods and h r t mperatures are retions were clear, transparent and brilliant. They quired than when the alkyl halide is an iodide possessed a high degree of flexibility and t or bromide. ness. Similar improved results may be obtained The dibutyl paraflin phosphonates are readily by any of the dibutyl alkane phosphonates havh'ydrolyzed by treatment with concentrated hying from 8 to 18 carbon atoms in the acid pordrochloric acid in an open vessel to yield the corti of t m Dibutyl butane phogphoe pon spa aflin p os nic acids. ylns nates are not suitable for this purpose. the procedure shown above for the preparation of n-hexanephosphonic acid, the following paraf- Example 3 fin ph'osphonic acids were obtained in a high de- Deslzed cotton fabric was lmpremwd the gree of purity: extent of 5 per cent by weight with dibutyl decanephosphonate, a hexane solution of the ester Paratln phosphonic acid m i being employed as the lmpres ating medium.

' The resulting dried, treated cloth showed an im- Ethm 6H provement in both feel and hand. n-Butane 103.4-4 While the invention has been described with zigz g w-kg particular reference to specific embodiments, it n-neptsnjl ins-3.5 is to be understood that it is not to be limited g gg gf f 53 3 00 thereto but is to be construed broadly and ren-neme ljj 102-25 stricted solely by the scope of the appended assess-.1 as claimsn-Hexadecane 94. 5-5. 5 What I claim 18! 'Oetadmne; 1. The process for preparing dibutyl esters of alkane ph'osphonic acids which comprises mixing The present method for the preparation of together an alkyl halide and sodiumdibutyl phosdibutyl paraflln phosphonates thus provides a phite until sodium halide has separated therecommercial, economically feasible process for the from, removing the separated sodium halide and manufacture of the individual, substantially pure then distilling the mixture to recover a dibutyl paraflin phosphonic acids, these free acids being aikane phosph'onate. obtainable in substantially quantitative yields by 2. The process for preparing dibutyl esters of hydrolysis of the dibutyl esters. Of these free alkane phosphonic acids which comprises mix acids, those having from 10 to 16 carbon atoms, ing together an alkyl halide and sodium dibutyl or the alkali metal salts of such acids, are highly phosphite, heating said mixture until sodium valuable as detersive and wetting-out agents. 76 halide h'as separated therefrom, removing the separated sodium halide from the mixture and then distilling the mixture to recover a dibutyl alkane phosphonate.

3. The process for preparing dibutyl esters of alkane phosphonic acids which comprises mixing together an alkyl halide and sodium dibutyl phosphite, heating said mixture while agitating the same until sodium halide has separated therefrom, washing said mixture with water to remove sodium halide and then distilling the residue to recover a. dibutyl alkane phosphonate.

4. The process for preparing dibutyl esters of alkane phosphonic acids which comprises mixing together an alkyl halide and sodium dibutyl phosphite, heating said mixture while agitating the same until sodium halide has separated therefrom, filtering said mixture to remove separated sodium halide and then distilling the filtrate to recover a dibutyl alkane phosphonate.

5. The process for preparing dibutyl esters of alkane phosphonic acids which comprises mixing together a primary alkyl halide and sodium dibutyl phosphite, separating a solid phase of sodium halide therefrom and then distilling the mixture dium bromide therefrom and then distilling the, 30

mixture to recover a dibutyl alkane phosphonate.

7. The process for preparing dibutyl decane phosphonate which comprises heating a mixture or n-decane bromide and sodium dibutyl phosphite, separating crystalline sodium bromide from the reaction mass and then distilling the organic residue to recover dibutyl decane phosphonate.

' the reaction mass and then distilling the organic residue to recover dibutyl dodecane phosphonate.

9. The process for preparing dibutyl tetradecane phosphonate which comprises-heating a mixture of tetradecane bromide and sodium dibutyl phosphite, separating crystalline sodium bromide from the reaction mass and then distilling the organic residue to recover dibutyl tetradecane phosphonate.

10. Dibutyl alkane phosphonates of the for- {A mula:

where R is an alkane radical having. at least 8 carbon atoms but less than 19 carbon atoms.

11. Dibutyl decane phosphonate. 12. Dibutyl dodecane phosphonate. 13. Dibutyl tetradecane phosphonate.

GENNADY M. KOSOLAPOFF. 

